This invention relates to a magnetic disk unit which mounts a plurality of magnetic disks and which equalizes temperature differences between individual magnetic disks.
A typical magnetic disk unit employs a plurality of magnetic recording disks stacked concentrically at predetermined intervals and rotates them at a predetermined number of rotations, and positions the magnetic head for each magnetic recording disk for magnetic recording (data entry) or reproduction (data reading).
In the case of such a magnetic disk unit, respective magnetic recording disks are mounted on the same spindle and are driven by the same driving source. Simultaneously, one or more magnetic heads are provided at each magnetic recording surface of each magnetic recording disk and these magnetic heads move together with respect to the disks because they are also driven by the same driving souce. On the other hand, such a magnetic disk unit provides only one surface of magnetic recording disk for recording the positioning servo information for positioning the magnetic head at the desired area on the magnetic recording surface of each magnetic recording disk. Therefore, entry and reading of information to/from the desired area of the desired magnetic recording surface can be done as follows. While a magnetic head reads the positioning servo information from the correspondng magnetic recording disk surface, another magnetic head driven by the same driving source is moved to the desired area and positioned therein.
Such a magnetic disk unit is required to have remarkable accuracy for positioning the magnetic head in the desired area.
Presently, magnetic disk units have the following problem with respect to high accuracy in positioning. Namely, the recording surface of the magnetic recording disk recording the servo information and the recording surface of the other magnetic recording disks used for ordinary data entry and reading are in different corresponding relationships.
This will be explained in detail. If the recording surface of the magnetic recording disk recording the servo information and the recording surface of a magnetic recording disk for ordinary data entry and reading are in different corresponding relationships on the occasion of positioning the magnetic head at the desired area in order to enter/read the data to/from the desired area of the magnetic disk, the enter/read magnetic head is not accurately positioned at the desired recording surface even if the servo magnetic head is positioned accurately at the recording surface of the magnetic disk recording the servo information. This problem results, to a considerable degree, from temperature differences between the magnetic recording disks.
Existing magnetic recording disks often uses aluminium as the basic material and therefore the difference in thermal expansion due to temperature differences is the principal cause of the problem.
Therefore, measures have been taken with the existing magnetic disk unit, so that the temperature distribution becomes equal at least within the shroud or cover by accommodating a plurality of magnetic recording disks in the shroud and circulating air within the shroud by the centrifugal force generated due to rotation of the magnetic recording disks. In such a structure, the air is introduce from the area near the spindle mounting the magnetic recording disks and this air is released between respective magnetic recording disks.
However, this existing air circulating system has a disadvantage in that temperature cannot be prefectly equalized because the air flows unequally between respective magnetic recording disks. As a result, it has been impossible for the existing magnetic disk unit to sufficiently reduce temperature differences between respective magnetic recording disks.